AFAIK, the FQDN is used for connecting to the registry, but it's not passed to the registry. So when you pull `ecr.example.com/namespace/project` the daemon co

AFAIK, the FQDN is used for connecting to the registry, but it's not passed to the registry. So when you pull `ecr.example.com/namespace/project` the daemon connects to `ecr.example.com`, but the registry only sees `namespace/project`. There was an old proposal [1] to pass the FQDN to the registry. That would allow for an auto-magical pull through cache / mirror combo along the lines of what you're asking about. For now I use a Nexus as a pull through cache, so `hub.example.com/library/image` is an image from Docker Hub where I want it to come through the cache. Anything that's important enough to have a local copy gets pulled/pushed into my private registry. I actually find the distinction between the cache (volatile) and the registry (non-volatile) to be useful. If I had to take a guess as to why Docker stubbornly clung to the current system it's that it's adhesive. Once you start using an alternate registry for base images, etc. it becomes really tough to swap to another one. The big mistake there is that instead of being the go to destination for public images, everyone is wholesale switching to the registry from their preferred cloud provider. 1. https://github.com/docker/distribution/issues/1620 https://github.com/docker/distribution/issues/1620